Colt M4 Flat top stripped upper receiver

[ybrik]

Purchased this new in gunbroker couple of months ago and would like to get more info on it.

Right side with black finish:
http://i6.photobucket.com/albums/y214/ybrik_5/DSC_1149__zps8c769beb.jpg (http://s6.photobucket.com/user/ybrik_5/media/DSC_1149__zps8c769beb.jpg.html)

Stamped "C" and keyhole/Cerro Forge:
http://i6.photobucket.com/albums/y214/ybrik_5/DSC_1148__zps32611ee5.jpg (http://s6.photobucket.com/user/ybrik_5/media/DSC_1148__zps32611ee5.jpg.html)

bottom/underside with grayish finish:
http://i6.photobucket.com/albums/y214/ybrik_5/DSC_1159__zps01e70d6a.jpg (http://s6.photobucket.com/user/ybrik_5/media/DSC_1159__zps01e70d6a.jpg.html)

Although not pictured, it is marked "M4" on one end of the picatinny railI have a Colt LE6920 rifle and the insides were all finished in black. This is the first time I have seen it in gray. Is this a legit stripped upper?

[Press Check]

The gray interior is a dry film lubricant coating to reduce friction. Most Colt receivers have the M4 marking above the gas tube hole, but it's not an absolute.

[Iraqgunz]

Asked and answered. Never seen an upper marked with a C that wasn't a Colt.